123I-Metaiodobenzylguanidine (123I-MIBG) scintigraphy scanning is commonly used in the imaging of phaeochromocytoma (and paraganglioma) to confirm the site of disease and whether any spread has occurred. However, 123I-MIBG imaging is negative in 15% of cases of benign phaeochromocytoma and around 50% of cases of malignant phaeochromocytoma. In recent years, positron emission tomography (PET) scanning using various different radiotracers has been shown to be a good alternative or supplementary investigation in phaeochromocytoma. We present the cases of four patients with symptoms and signs suggestive of phaeochromocytoma, but who had negative 123I-MIBG scans, and illustrate the usefulness of 18-fluoro-dihydroxyphenylalanine PET scanning in their assessment. In one of the patients, we illustrate how fluorodeoxyglucose PET scanning can provide useful information about the extent of malignant disease. These illustrative cases lend further support for the use of PET scanning in the assessment of phaeochromocytoma and suggest that it may have a particularly important role in the investigation of patients in whom 123I-MIBG scanning is negative.